DESCRIPTION: (provided by the applicant): Our long-term goal is to understand how the steroid ecdysone and the sesquiterpenoid juvenile hormone (JET) act at the cellular and molecular level to coordinate insect growth, molting and metamorphosis. Ecdysone causes molting and the genetic switches necessary for metamorphosis, while JR prevents these switches but does not interfere with molting. To elucidate the nature of this action of JET, we will concentrate on how it regulates the expression of the ecdysone-induced cascade of transcription factors that initiate the molt in the epidermis and its derivatives, primarily the "early" genes E74, E75, and BroadComplex (BR-C), the latter of which appears only at metamorphosis. These studies will use both Drosophila and the tobacco hornworm Manduca sexta, since the effects of JR are well defined in Manduca where the epidermis expresses a larval program of differentiation in the presence of JH, then at metamorphosis in its absence switches to a pupal program then an adult program. The abdominal histoblasts of Drosophila show a similar response to JET so that we can use the techniques of Drosophila genetics. Our specific aims over the next 5 years are: 1) To study the function of the ecdysone-induced BR-C transcription factors as pupal-specific factors regulating cuticle synthesis in both Drosophila and Manduca, using mis-expression and deletion techniques. 2) To study the regulation of BR-C by JET in Drosophila at both the morphological and the molecular level. 3) To study the regulation of the ecdysone-induced transcription factor E74 by JR and compare it with that of E75. 4) To elucidate the molecular basis of the JR-induced suppression of the eye primordium during larval development of Manduca. 5) To look for other JR-regulated genes in Drosophila using a Drosophila gene chip. Switches in gene expression are common in development and usually are mediated by various signaling molecules. A deeper understanding of the action of JR in directing the DNA regulatory actions of a steroid should enhance our understanding of how retinoids and other small lipophilic molecules may regulate vertebrate development. It is also Important for the design of new types of insect growth regulators to control insect vectors of disease.